The application of lithium currently extends to diverse industries, including the rechargeable battery, glass, ceramic, alloy, lubricant, and pharmaceutical industries. The rechargeable lithium battery has recently been receiving attention as a main power source for hybrid and electric cars, and the market for lithium rechargeable batteries for cars is expected to continue growing to approximately one-hundred times the conventional compact battery markets for cell phones and notebooks.
In addition, a global movement towards more stringent environmental regulations is likely to expand the application of lithium to not only the hybrid and electric car industries, but to the electrical, chemical and energy fields as well. Thus, a dramatic increase of both domestic and foreign demand for lithium is expected.
The main sources for the lithium could be minerals, brine and seawater. Although minerals such as spodumene, petalite and lepidolite contain relatively large amounts of lithium, ranging from approximately 1 to 1.5%, the extraction involves complicated processes such as floatation, calcination at a high temperature, grinding, acid mixing, extraction, purification, concentration, and precipitation. These processes, require high energy consumption, are considered to be cost-ineffective, and the use of acids during the lithium extraction also causes environmental pollution.
It has been reported that approximately 2.5 1011 tons of lithium is dissolved in seawater. Although the majority of technologies involve inserting an extraction device containing an absorbent into the seawater in order to extract lithium by treating with acids after selectively absorbing the lithium, it is extremely inefficient and uneconomical to directly extract the lithium from seawater because the concentration of lithium contained in the seawater is limited to 0.17 ppm.
Due to the aforementioned disadvantages, lithium is currently extracted from brine produced from natural salt lakes, but salts such as Mg, Ca, B, Na, K, SO4 are also dissolved in the brine.
Further, the concentration of lithium contained in the brine ranges from approximately 0.3 to 1.5 g/L, and lithium contained in the brine is usually extracted in the form of lithium carbonate having a solubility of about 13 g/L. Even assuming that lithium contained in the brine is completely converted to lithium carbonate, the concentration of lithium carbonate in the brine is limited to 1.59 to 7.95 g/L (the molecular weight of Li2CO3 is 74, and the atomic weight of Li is 7. If the concentration of lithium is multiplied by 5.3 (74 14≈3), the concentration of lithium carbonate can be estimated). Since most of the lithium carbonate concentration is lower than the solubility of lithium carbonate, the extracted lithium carbonate re-dissolves, a solid may be difficult to be separated from a liquid, and thus there is a problem of the lithium extraction yield being extremely low.
Accordingly, in order to extract lithium carbonate from lithium contained in brine, the brine pumped from the natural salt lake was stored in evaporation ponds and subsequently naturally evaporated outdoors over a long period of time, for instance several months to about one year, to concentrate the lithium by several tenfold. Then, the impurities such as magnesium, calcium, boron were precipitated in order to be removed, and the method required an amount greater than the solubility of lithium carbonate to precipitate.
For instance, Chinese Patent Pub. No. 1,626,443 describes a method of extracting lithium, wherein brine is evaporated and concentrated under solar heat, and the concentrate is subject to repeated electro-dialysis in order to obtain brine containing concentrated lithium with a low amount of magnesium.
Such conventional methods require the evaporation and concentration of the brine, which are consuming of energy and time, and unproductive, especially during rainy seasons. Further, the loss of lithium is unavoidable when lithium is precipitated along with other impurities in the form of a salt.